Preparation of Ti 2 CuAl 5 by Reactive Sintering

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PREPARATION OF Ti2CuA15 BY REACTIVE SINTERING ARNULF J MAELAND* AND DAVE NARASIMHAN* *Corporate Technology, 07960

Allied-Signal

Inc.,

Morristown,

NJ

ABSTRACT The exothermic formation of intermetallic compounds from the constituent powders through reactive sintering at relatively low temperatures is a promising new process being explored The process is for the preparation of nickel aluminides. useful for synthesis of other intermetallics as well. We describe here the preparation of Ti2CuAl5 using the technique of reactive sintering. This intermetallic compound has a L12 structure which is also the structure of the very Characterization of the interesting Ni3Al intermetallic. Ti2CuAl5 phase is done by x-ray diffraction, microhardness, and microstructure. INTRODUCTION Titanium and nickel aluminides are being considered as structural materials in high temperature applications due to a favorable combination of density, strength, oxidation resistance and low cost. However, while some single crystal aluminides may be ductile, the polycrystalline aluminides are consequently brittle and makes processing and manufacturing Ni3Al which has the of parts difficult if not impossible. L12 structure, is of special interest because addition of boron has been shown to produce significant increase in ductility(l). In addition Ni3Al exhibit positive (anamolous) temperature dependence of strength, i.e., the strength increases with temperature(2) . The corresponding titanium aluminide, Ti3Al, does not have the L12 structure, but a hexagonal DOl9-type structure. However, AI3Ti has a tetregonal D022-type structure which is related to the L12 structure(3), and replacement of a certain amount of Al in AI3Ti with Cu is known to transform the D022 structure into the L12 structure (4,5). Santandrea et al. (6) reported two years ago at the MRS HighTemperature Ordered Intermetallic Alloys Symposium that single phase nickel-aluminum intermetallic compounds, including Ni3AI, could be prepared from mixtures of spherical powders of the elements by heating to 1100K. The process involves the formation of a transient liquid phase during the highly exothermic reaction between the metal powders(7). The process has been referred to as reactive sintering and has been studied in considerable details in connection with the preparation of Ni3Al from elemental mixtures of nickel and aluminum(8-10). We have used a modified reactive sintering process to prepare Ti2CuAl5. This intermetallic compound correspond to the composition when sufficient Al has been replaced with Cu in Al3Ti to produce the L12 structure. Mat. Res. Soc. Symp. Proc. Vol. 133. -1989 Materials Research Society

724

EXPERIMENTAL The intermetallic compound Ti2Cu was used as starting material rather than elemental Ti and Cu. Spherical, 20 micron aluminum powder was thoroughly mixed with